A commonly assigned U.S. Pat. No. 4,356,317 of Coleman, Hallcher and McMackins, issued Oct. 26, 1982, describes a procedure to react butadiene and acetic acid with metal ion oxidant to prepare acetoxyhexenoic acids. A U.S. Pat. No. 4,175,089 describes a procedure for reacting olefins and acetic acid with metal ion oxidant to produce lactones. The prior procedures are generally conducted in solvents, e.g. in acetic acid, and separation of product generally involves extraction procedures. Particular separation procedures for .gamma.-butyrolactones are described in U.S. Pat. No. 3,992,417. One of the characteristics of prior procedures, particularly those directed to production of acetoxyhexenoic acids, is that initially good selectivity to desired product tends to decline as conversions are increased, or as product concentrations in the reaction mixture are increased. Consequently it may be necessary to operate such processes at economically poor payloads or to develop possibly expensive processing means to retain appropriate selectivity. It has been found that .gamma.-vinyl-.gamma.-butyrolactone is more stable under preparation and isolation conditions than acetoxyhexenoic acids. Procedures for preparing acetoxyhexenoic acids and converting the acids to .gamma.-vinyl-.gamma.-butyrolactone are described and claimed in a simultaneously filed, commonly assigned application of Coleman et al, Ser. No. 503,979. In such procedures with continuous conversion of acetoxyhexenoic acids to .gamma.-vinyl-.gamma.-butyrolactone, it is feasible to keep the acetoxyhexenoic acid content at a low level but operate at a relatively high total payload of acetoxyhexenoic acids plus lactone, with minimal loss of chemical yield and current efficiency. However, such procedures generally require additional equipment with consequent costs and add complexity to the process because of the additional reactions involved. A related commonly assigned application of Coleman and McMackins, simultaneously filed with the present application, Ser. No. 503,982, involves reactions of butadiene and acetic acid with metal oxidant in solvent medium, followed by a separation procedure in which product is separated from molten salt electrolyte.